The present invention relates to a lamp base locking clip, a method of making the clip and a lamp base shell assembly which utilizes the clip.
Most lamps utilize lamp base shells to facilitate insertion and removal into a complementary lamp socket, and to establish electrical contact between the lamp and the socket. Several structures have been developed to prevent the lamp base shell from separating from the lamp base, particularly when the lamp is removed from the socket at the end of its useful life. See, for example, U.S. Pat. Nos. 1,262,936; 2,028,884; 2,157,051; and 5,006,751.
In another configuration, a threaded inner shell having a washer-like base and a plurality of orthogonally projecting tabs around the base's periphery is used to secure the lamp base shell. The inner shell's tabs each have a dimple, or indentation, which corresponds with dimples molded in the neck of the lamp base. The inner shell is secured to the lamp base by placing it over the base until the corresponding dimples are mated. Once the inner shell is in place, a lamp base shell is securely screwed onto the inner shell and is staked, or pierced, to engage it with the inner shell. Inner shells are generally made from any non corrosive steel, such as a nickel-iron alloy, to prevent breakdown. Furthermore, lamps typically have two lead wires. A side lead wire is attached to the outer surface of the inner shell prior to the securing and staking of the lamp base shell, for example, by soldering or welding. A center lead wire typically passes through an eyelet where it is attached, also by soldering or welding. This configuration, while securing the lamp base shell, and providing electrical contact, requires several parts and difficult manual assembly, particularly with respect to attaching the side lead wire to the surface of the inner shell. This approach results in costly, time consuming, and inefficient lamp production.
Another method to electrically connect the lamp's lead wires to the lamp base shell, and mechanically secure the base shell to the lamp base, uses a threaded form molded into the lamp glass with a keyway to accommodate a lead solder preform that makes the required electrical connection and locks the base onto the glass.
Although providing sufficient backout torque resistance to meet applicable standards and requirements, and addressing deficiencies of the inner shell technique, use of lead solder has several disadvantages. First, lead solder is an environmental pollutant. Therefore, as environmental laws and regulations continue to impose new and increasingly stringent standards, the lamp industry is attempting to phase out the use of lead solder. Second, the use of lead solder increases both direct and indirect costs associated with lamp production. Lead solder is an expensive material and, further, soldering discolors the brass or coppernickel alloy base shells typically used in high intensity discharge lamp applications. More expensive nickel-plated base shells must be used to maintain good aesthetics, thereby increasing the overall cost of lamp production.
An attempt to obviate the above disadvantages is shown in pending U.S. patent application Ser. No. 08/139,474, now U.S. Pat. No. 5,381,070. This approach works well in smaller bulb sizes and eliminates the use of solder; however, it can sometimes fail torque tests in larger size bases, such as the mogul base.
It is, therefore, an object of the invention to obviate the disadvantages of the prior art.
It is another object of the present invention to provide a lamp base locking apparatus and method which is cost effective and provides for an efficient assembly line operation.
It is a further object of the present invention to provide a lamp base locking apparatus and method which is environmentally safe while not increasing lamp manufacturing costs.